An optical disc (optical recording medium) such as a CD or DVD is normally manufactured by forming thin films such as a light reflecting layer by sputtering or the like on a disc-like substrate in whose surface grooves and lands have been formed by injection molding and then forming a resin layer as a protective layer (cover layer) by spin coating so as to cover the thin films. Also, when manufacturing a recordable optical disc such as a CD-R, a CD-RW, a DVD-R, and a DVD-RW, after thin films such as a recording layer and a light reflecting layer have been formed in order by sputtering or the like on the surface of a substrate, a resin layer as a protective layer is formed by spin coating so as to cover the thin films. When doing so, if fluctuations are produced in the thickness of the resin layer of a completed optical disc, it will be difficult to read and write recording data properly. Accordingly, when the resin layer is formed, it is necessary to spin coat a resin material for forming the resin layer across the entire substrate surface with a uniform thickness. To form a resin layer with a uniform thickness on a substrate by spin coating, the resin material should preferably be dripped onto a center of a substrate that is being rotated. However, since it is necessary to provide a center hole for clamping (chucking) in a recording/reproduction apparatus or the like in a center of the optical disc, it is difficult to drip the resin material at a center of the substrate during spin coating. For this reason, the applicant has developed a method of manufacturing an optical disc where a resin material is dripped to form a resin layer with a uniform thickness before the center hole is formed, and then the center hole is punched out so as to pass through the substrate and the resin layer.
More specifically, as shown in FIG. 14, a resin material is spin coated onto a surface 52a of a disc-like substrate 52, in a center of which a center hole has not been formed. When doing so, as shown by the broken line in FIG. 14, a UV-curing resin material, for example, is dripped onto a center (a position where the center hole will subsequently be formed) of the substrate 52 that is being rotated by an applying apparatus and the resin material spreads toward the outer edge of the substrate 52 due to the centrifugal force that accompanies the rotation. Here, by appropriately adjusting the rotational speed of the substrate 52, the resin material can be applied uniformly across the entire surface of the substrate 52. The resin material on the substrate 52 is then irradiated with UV rays to harden the resin material and thereby form a resin layer 53. After this, a cylindrical punching blade 65 for forming the center hole 51a is pressed into the substrate 52 in the direction of the arrow A from a rear surface 52b side to punch out the part shown by the broken line in FIG. 14. By doing so, as shown in FIG. 15, the center hole 51a with a diameter L1 of around 15 mm is formed so as to pass through the substrate 52 and the resin layer 53, thereby completing the optical disc 51.
On the other hand, Japanese Laid-Open Patent Publication No. H10-289489 discloses a method of manufacturing an optical recording medium where a light transmitting layer (18) is formed by dripping light-curing resin in a state where a center hole (10h) formed in a substrate (10) has been blocked by a blocking plate (21). In this method of manufacturing, a concave part (20) is formed in a periphery of the center hole when manufacturing the substrate, and when the light-curing resin is to be dripped, the blocking plate is fitted into this concave part to form a composite substrate and block the center hole. By doing so, it is possible to drip the light-curing resin on the center part of the substrate (in this case, the center part of the blocking plate). After the light-curing resin that has been dripped on the center part of the substrate has been spread out and cured with light, the blocking plate and the light transmitting resin are punched out by a center hole punching device (71) to form the center hole. By doing so, an optical recording medium is manufactured.